1. Field of the Invention
This invention relates to providing new green-emitting and yellow-emitting phosphor powders and white light emitting diodes (LEDs) that include solid solution phosphors.
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification by one or more reference numbers within brackets, e.g., [x]. A list of these different publications ordered according to these reference numbers can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)
For generating white light, most current commercial LED lamps employ yellow-emitting YAG:Ce3+ phosphors excited by blue InGaN diodes due to the unsurpassed efficiency such a combination provides [1-3]. However, YAG:Ce3+ phosphors have relatively weak emission in the red spectral region, and consequently the color rendering ability has yet to be improved [4-6]. In addition, the output color from YAG:Ce3+ phosphors is strongly dependent on temperature and current, which will become a significant problem in high-power LEDs [7]. To overcome these drawbacks, and also to avoid issues associated with intellectual property, there are extensive efforts worldwide to develop new yellow-emitting phosphors for blue-pumped LED applications [8-11] as well as to optimize the existing systems.
Unfortunately, with the exception of YAG:Ce3+, there are few phosphor materials for the long ultraviolet (UV) or blue excitation sources. Up to now, no competing yellow phosphor has been found replace to the YAG:Ce3+ phosphor. It is necessary to develop new phosphors in terms of phosphor efficiency and color rendering property in the red spectral region.
Thus, in order to address this issue, a new phosphor is required for solid-state lighting. The present invention can be used for white light generation by combining either a near UV-LED (peak emission wavelength λmax=395 and 405 nm) and red-emitting phosphor, or a near UV-LED and green-orange phosphors, or a near UV-LED and yellow phosphor. The present invention can also be used for white light generation by combining either a blue LED and yellow phosphors, or a blue LED and green-yellow phosphors, or a blue LED and yellow-red phosphors. For this purpose, there are many numbers of different applications.
In the present invention, one of end members, M3SiO5 (M=Ca, Sr, Ba), was developed by Blasse et al. [12] as a phosphor material for Eu2+ ions, and then Jang et al. [13] and patents [14, 15] reported the LED application (Korea Patent No. 2007-98275 and PCT/2009/0085467 respectively). Thus, in this disclosure, the present invention does not cover the end member of Sr3SiO5 corresponding to z=1.0 in a solid solution series between Sr3AlO4F and Sr3SiO5, (Sr3−x−yARy)(Al1−(z+u)IIIuSiz)O4+zF1−z:Ce3+x.